Puncture and abrasion resistant, air and water impervious laminated fabric

ABSTRACT

A puncture and abrasion resistant, air and water impervious laminated fabric is provided. The laminated fabric includes a woven fabric base layer having warp and weft yarns, with at least 50 percent of the fibers in the warp yarns being formed of high performance material. A first thermoplastic film is bonded by heat and pressure to at least one of the sides of the fabric base layer. The first thermoplastic film is formed of ethylene vinyl acetate. A second thermoplastic film is bonded by heat and pressure to the first thermoplastic film on at least one of sides of the fabric. The second thermoplastic film is formed from either high density polyethylene or low density polyethylene.

RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No.11/590,366 filed Oct. 31, 2006, entitled “Puncture and AbrasionResistant, Air and Water Impervious Laminated Fabric,” the content ofwhich is hereby incorporated in its entirety.

FIELD OF THE INVENTION

The present invention relates to puncture and abrasion resistantlaminates and the process for their production. More particularly, thepresent invention relates to a laminated high strength, high performancefabric made air and water impervious with multiple layers ofthermoplastic film comprising ethylene vinyl acetate (EVA) andpolyethylene.

BACKGROUND OF THE INVENTION

High performance fabrics have been used for numerous applications wheretear-resistance, abrasion-resistance, cut- and stab-resistance, andchemical- and cold-resistance are important. As used herein, the term“high performance” refers to fabrics constructed from a group of fibersused to make cut-resistant and abrasion resistant articles such as cableand rope covers, hovercraft curtains, gun and boat covers, gloves, andaprons. The high strength-to-weight ratios of these fabrics can provideproperties having significant improvements in the performancecharacteristics stated above at a fraction of the weight of otheralternatives.

It has been found desirable to combine the advantages of highperformance fabrics with thermoplastic film laminates for applicationswhere the fabric also must be air and water impervious. Fabrics for suchapplications were previously typically constructed from vinyl-coatednylon or similar materials which do not exhibit high performancecharacteristics.

Recently, a thermoplastic film such as EVA has been bonded to asubstrate of high performance fabric to create a more durable, cut andwear resistant flexible laminate that is also air and water impermeable.This high performance fabric is preferably constructed from an extendedchain polyethylene such as ultra high molecular weight polyethylene. EVAprovides a superior bond to the ultra high molecular weight polyethylenefabric; however, it has been found by the inventors that an EVA laminatebecomes soft and tacky when exposed to temperatures above about 120degrees Fahrenheit. As used herein, “tacky” refers to the property of amaterial wherein it is sticky and lacks a smooth, slick surface overwhich objects may slide with minimal friction. As will be appreciated bythose skilled in the materials arts, when a film becomes soft and tacky,it is not only susceptible to degradation, but also to damage caused byobjects that may impinge or otherwise impact the film. For example, afilm subject to such degradation would prove highly unsuitable in warmor hot environments that are subject to severe weather such as tropicalstorms or hurricanes. Further, the tacky condition will degrade anyoperation in which objects must move over or make contact with the film;e.g., a conveyor belt. While it has been found that both low and highdensity polyethylene may be subjected to such elevated temperatureswithout becoming soft or tacky, the inventors have also found thatpolyethylene does not provide the degree of bonding to certain highperformance fabrics, such as high molecular weight polyethylene fabrics,needed for certain applications. Thus, each of the two types ofthermoplastic film provides at least one superior physical property overthe other.

The inventors therefore have discovered a need then for a process thatsecurely and reliably bonds a thermoplastic film to a high molecularweight polyethylene fabric and that has an outer film surface that willnot degrade, become tacky, or soft under anticipated operationalconditions.

SUMMARY OF THE INVENTION

The present invention solves the problems previously attendant to thelamination of fabrics constructed with a substantial percentage of highperformance fibers such as high tenacity, high modulus, ultrahighmolecular weight polyethylene fibers. In general, the invention involvesa laminate having a combination of films (EVA and polyethylene) on oneor both sides of a base layer of high performance fabric, such asultra-high molecular weight polyethylene.

The puncture and abrasion resistant, air and water impervious laminatedfabric may be made through the application of pressure in a hydraulicpress. An inner layer of EVA thermoplastic film is laminated directly toa fabric comprised of ultra high molecular weigh polyethylene yarn. Anouter layer of polyethylene thermoplastic film is simultaneously bondedto the EVA layer. The laminating step is conducted at a temperature ofbetween about 200 degrees Fahrenheit and 285 degrees Fahrenheit with acontact time of between about 5 minutes and about 15 minutes and at alaminating pressure of between about 50 psi and 500 psi. The sameprocess can be used on a fabric having EVA and polyethylene film on bothsides.

A second solution, and aspect of the present invention, involves rollinga fabric formed of ultra high molecular weight polyethylene yarns, afirst layer of EVA thermoplastic film, and a second layer ofpolyethylene thermoplastic film together under tension to form a woundbundle with the fabric of high performance yarns placed on the outside.The wound bundle is then heated at a temperature of between about 200degrees Fahrenheit and 285 degrees Fahrenheit and for a sufficientlength of time of between about 8 hours and 18 hours. This softens boththe EVA and the polyethylene films such that as the high performancefibers shrink, the fabric, EVA, and polyethylene will laminate and bondtogether, and such that the EVA will bond to the fabric, to create athree layer laminated construction.

Both of these techniques result in a flexible, puncture and abrasionresistant, substantially air and liquid impervious laminate that holdsup well at elevated temperatures.

These and other aspects of the present invention will become apparent tothose skilled in the art after a reading of the following description ofthe preferred embodiments when considered in conjunction with thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the laminate being formed by oneexemplary lamination process of the present invention;

FIG. 2 is a schematic representation of the laminate being formed by asecond exemplary lamination process of the present invention; and

FIG. 3 is a more detailed schematic representation of the laminationprocess of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the term “fabric” includes plain weave fabricsconstructed using convention weaving techniques.

The term “fiber” as used herein refers to a fundamental component usedin the assembly of yarns and fabrics. Generally a fiber is a componentwhich has a length dimension which is much greater than its diameter orwidth. This term includes monofilament, multi-filament, ribbon, strip,staple, and other forms of chopped, cut or discontinuous fiber and thelike having a regular or irregular crossection. “Fiber” also includes aplurality of any one of the above or a combination of the above.

As used herein the term “high performance fiber” means that class offibers having high values of tenacity (greater than 7 g/d) such thatthey lend themselves for applications where high abrasion and/or cutresistance is important. Typically, high performance fibers have a veryhigh degree of molecular orientation and crystallinity in the finalfiber structure.

As used herein the term “high performance fabric” means a fabricconstructed using a high performance fiber as a major constituent of thefabric such that the fabric enjoys the performance benefits of the highperformance fibers. Thus, in an embodiment, a fabric constructed of 100%high performance fiber is a high performance fabric. In otherembodiments, the high performance fabric may be made up of less than100% high performance fibers. For example, a woven fabric in which atleast about 50 percent of the warp yarns, or 50 percent of the fibers inthe warp yarns, are comprised of a suitable high performance fiber meetsthis definition for the purposes of the present invention. The remainingwarp yarns and the fill yarns may be comprised of any other suitablematerial that is compatible with the practice of the present invention.

The cross-sectional shapes of fibers suitable for the practice of thepresent invention include circular, flat or oblong. They may also be ofirregular or regular multi-lobal cross-section having one or moreregular or irregular lobes projecting from the linear or longitudinalaxis of the filament.

As used herein the terms laminate and laminating refer to theapplication of a flexible film to a fabric construction to form alasting bond that will hold up to rough usage without delamination.

Suitable high tenacity, high modulus fibers are solution-drawn,ultra-high molecular weight (UHWM) polyethylene fibers, such as thosesold under the brand names Spectra®, Dyneema® and Tekmilon®. Further itis believed that melt spun polyethylene fibers with a tenacity of 15grams per denier, such as Certran® fibers, can be laminated but may notprovide the same film adhesion. Also, aramid fibers such as Kevlar®(DuPont) is believed to provide a suitable fiber for the base layer.

It has been found that polyethylene and ethylene vinyl acetate (EVA)films can be made to adhere to fabrics constructed from ultra highmolecular weight polyethylene (UHMWPE) fibers without the use of abonding agent under appropriate laminating conditions. Any suitable EVAfilm can be used as the film for lamination directly to the UHMWPEfabric. It has now been found that high-density polyethylene,low-density polyethylene and linear low-density polyethylene films willbond well onto EVA and are thus suitable for use as the outer layer(s)in the practice of the present invention. More specifically, in theexamples that follow, EVA is used as the thermoplastic film/materialthat is laminated directly to the fabric since EVA has been found tohave superior bonding with the fabric. A polyethylene film, which bondsquite well with EVA under certain laminating conditions, is used as theouter laminate layer since it can withstand higher operationaltemperatures without the degradation described above, and thus prevent atacky surface as may be experienced by an EVA outer layer in someenvironments.

The following methods for forming the composite laminated fabricconstruction comprise the application of heat and/or pressure to thefabric and lamination films for a given time.

In a first aspect of the present invention, illustrated schematically inFIG. 1, the application of heat and pressure is accomplished by means ofa flat hydraulic press 10. Positioned between the upper 12 and lower 14press members are a fabric sheet 30 formed of ultra high molecularweight polyethylene yarns, a first lamination film 20 of EVA 20, and asecond, or outer lamination film 25 of low or high density polyethylene.As shown in FIG. 1, both sides of the fabric sheet 30 are laminated withthe two film layers; however, the two film layers may be laminated toonly a single side of the fabric sheet 30 if desired. The press members12, 14 clamp the fabric sheet 30, EVA film 20 and polyethylene film 25under varying conditions of heat, pressure, and time. A suitable pressfor the practice of the present invention is the Wabash Model MPIV50H-18-BC. The practice of the present invention also includes the useas necessary of a suitable release paper between the outer polyethylenelayer 25 and the hydraulic press platens to prevent heat damage to thefabric surface.

More particularly, the variable conditions for lamination with ahydraulic press of this type comprise: (1) the fabric construction, (2)thicknesses of the film layers 20, 25, (3) the pressure applied by thepress members 12, 14, (4) the temperature applied by the press members,and (5) the time that the pressure and temperature are applied. Thefabric used in the present invention is formed from high performanceyarns having a denier between about 360 and about 1,200. The EVA film 20has an initial thickness of between about 2 mils and about 8 mils, anddesirably between 4 mils and 8 mils. The polyethylene film 25 has aninitial thickness of between about 1.5 mils and 20 mils, and isdesirably between about 1.5 and 2 mils. The desirable temperature rangeis between about 200 degrees Fahrenheit and 285 degrees Fahrenheit.Pressure is applied between about 50 psi and about 500 psi. Lastly,contact time is between about 5 minutes and about 15 minutes. Additionalheating in an oven may further enhance the bonding between the EVA andthe fabric, and between the EVA and the polyethylene.

Alternatively, the lamination process of the present invention may beperformed by first rolling the fabric and film layers into a tight roll.The pressure applied to create the lamination of the layers results fromthe combination of first rolling the fabric, EVA film, and thepolyethylene film into a tight roll with the fabric positionedexteriorly of the films, and by the pressure generated by shrinkage ofthe fabric fibers during heating. Temperatures for heating the roll inan oven may vary between about 200 degrees Fahrenheit and about 285degrees Fahrenheit, depending on the type of polyethylene thermoplasticfilm used. Heating time varies from about 8 hours to about 18 hoursdepending upon the temperature selected. Thus, as the processtemperature is increased, process time is reduced. Conversely, at lowerprocess temperatures, the time required to create a usable film tofabric bond and film to film bond increases rapidly. The minimumacceptable temperature is that which is sufficient to soften the filmsand to create a sufficient laminating pressure.

This alternative lamination process may be conducted using a three-stepprocess as illustrated in FIGS. 2 and 3. The first step includes firstsimultaneously tacking the thermoplastic polyethylene film 25 and theEVA film 20 to the fabric construction 52 on a continuous basis using aheated calendar roll 54 to form a lightly laminated three-plyconstruction. After this step, the polyethylene film 25, EVA film 20,and fabric 52 are uniformly adhered, but can be separated easily. Inthis condition the high performance fabric/EVA film/polyethylene filmcombination is not suitable for the proposed end uses contemplated forthe present invention. A release paper 58 may be used if desired. Asuitable machine is the Van Vlandrin Silk Calender with a husk soft rolland a heated steel center roll. Older versions of this machine are steamheated and have provision for modifying the amount of pressure appliedto the film/fabric combination. After the tacking step, the continuousroll is wound tightly into a bundle 56 with appropriate release paper 58and secured with heat resistant tape. In this example, the release paper58 is positioned so as to be directly adjacent the paper core 300 duringwindup. Next, the bundle is baked in an oven for between about 8 hoursand about 18 hours at a temperature between about 200 degrees Fahrenheitand about 285 degrees Fahrenheit. In this embodiment, pressure isapplied to the film/fabric in one of two ways: (1) first at a moderatetemperature and a relatively high pressure for a short duration, or (2)at a second much lower pressure for a much longer duration.

More particularly, as shown in the embodiment of FIG. 3, only one sideof the fabric 312 is laminated. The fabric 312 and two film layers (20,25), shown collectively as 311, are tightly rolled onto a paper core 300having a diameter of between about 2 to 6 inches with a release paper310 to form a bundle 315. The fabric 312 and film layers 311 arearranged so that the fabric 312 is positioned outwardly of the film.This is so that the force generated by the shrinkage of the fabricduring heating will force the three component layers into laminatingcontact. Although reversing the position of the fabric and film may beacceptable, the better performance is achieved using the arrangementdescribed above. The resulting bundle 315 is then secured with a tapecapable of withstanding the laminating temperature. The wound bundle 315is then heated to about between 200° F. and about 285° F. for a periodof between about 8 hours and about 18 hours. Preferably, the heattreatment is conducted at a temperature of about 265° F. for about 18hours. Here the primary laminating pressure is applied to the bundle bythe fabric shrinkage that occurs during heating. The exact amount ofpressure is unknown but is believed to be under 50 psi. Extra pressurebeyond that generated by the act of forming the bundle may be appliedduring the heat treatment but is not required for acceptable results.

The laminates of the present invention may also be made using machinesdesigned for other purposes. By way of non-limiting example, theapparatus disclosed in U.S. Pat. No. 5,401,344 to Dickson et al. forproducing rolls of wrinkle free composite sheet material may be used.Dickson discloses a curing apparatus including a cylinder with aninternally lined inflatable bladder. The cylinder is adaptable to bemoved into surrounding relation with a sheet material. A forming roll isarranged to supply heat from the interior of the assembled wraps ofmaterial while the surrounding inflated bladder exerts pressure to curea ballistics-type material over a pre-determined cure cycle. Thepractice of the present invention does not involve a “curing” time perse. However, the ability to provide a controlled heating step andwrinkle-free final product are useful for the practice of the presentinvention. The content of the Dickson et al. patent is incorporatedherein by reference in its entirety.

The following examples are exemplary of fabric, film, and laminationparameters that may be selected to practice the two methods of thepresent invention. The specific process parameters, i.e., temperature,pressure, time and materials illustrate the invention in an exemplaryfashion and should not be construed as limiting the scope of theinvention. In each of the examples, the fabric is constructed using 100%high performance fiber. The style designations used in the examples arewell-known product references commonly used in the art.

Example 1

A laminated fabric was produced by pressing a 17×17, plain weave fabric,style 902, woven from 1200 denier weight Spectra® 900 yarn with an EVAfilm and outer low density polyethylene film. The two films had a totalthickness of about 8 mils. The three layers were subjected to ahydraulic press for five minutes at a temperature of 230 degreesFahrenheit at 50 pounds per square inch.

Example 2

A laminated fabric was produced by pressing a 34×34, plain weave fabric,style 904 woven from 650 denier weight Spectra® 900 yarn with an EVAfilm and outer low density polyethylene film. The two films had a totalthickness of about 8 mils. The press temperature was 280 degreesFahrenheit and the pressure was 150 PSI. The time under pressure andheat was five minutes.

Example 3

A laminated fabric was produced by rolling together a 17×17 plain weavefabric, style 900, with an EVA film, an outer low density polyethylenefilm, and a 0.5 mil polyester release paper. The two films had a totalthickness of about 8 mils. The tightly wound roll was wrapped with heatresistant tape and heated in an oven at 265 degrees Fahrenheit for 18hours.

Example 4

A laminated fabric was produced from a fabric formed from Spectra®yarns, style 904, woven from 650 denier weight Spectra® 900. EVA and lowdensity polyethylene films having a combined thickness of 8 milscomprised the laminates. These components were wound tightly on a papercore along with a 0.5 mil Mylar® release film. The resulting roll wasmaintained under tension as it was secured with a suitable tape. Theroll was heated at 275° F. for 18 hours. The film was uniformlylaminated to the fabric.

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be utilized without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchmodifications and variations are considered to be within the purview andscope of the appended claims and their equivalents.

1.-3. (canceled)
 4. A method for making a puncture and abrasionresistant, air and water impervious laminated fabric, comprising: (a)providing a fabric in which high performance yarns are a majorconstituent thereof, the yarns being selected from the group consistingof extended chain polyethylene, ultra high molecular weightpolyethylene, and aramids and having a denier between about 360 and1,200; (b) positioning a first thermoplastic film over at least one sideof the fabric, the thermoplastic film comprising ethylene vinyl acetateand having a thickness of between about 2 and 8 mils; (c) positioning asecond thermoplastic film over the first thermoplastic film on at leastone of the first and second sides of the fabric, the secondthermoplastic film selected from the group consisting of high densitypolyethylene and low density polyethylene and having a thickness ofbetween about 1.5 and 20 mils; (d) applying a pressure of between about50 and 500 psi to the laminated fabric and thermoplastic film at atemperature between about 200 degrees Fahrenheit and 285 degreesFahrenheit; and (e) maintaining the pressure and temperature for betweenabout 5 minutes and 15 minutes so that the second thermoplastic filmsoftens and bonds to the first thermoplastic film.
 5. The method ofclaim 4 further including the step of tacking the first and secondthermoplastic films over at least one of the first and second sides ofthe fabric before step (d).
 6. A method for making a puncture andabrasion resistant, air and water impervious laminated fabric,comprising: (a) positioning a first thermoplastic film comprisingethylene vinyl acetate over at least one side of a fabric comprised of ahigh performance yarns, the yarns being selected from the groupconsisting of extended chain polyethylene, ultra high molecular weightpolyethylene, and aramids and having a denier between about 360 and1,200, the first thermoplastic film having a thickness of between about2 and 8 mils; (b) positioning a second thermoplastic film over the firstthermoplastic film on at least one of the first and second sides of thefabric, the second thermoplastic film selected from the group consistingof high density polyethylene and low density polyethylene and having athickness of between about 1.5 and 20 mils; (c) rolling the fabric,first thermoplastic film, and second thermoplastic film together undertension to form a wound bundle; and (d) heating the wound bundle at asufficient temperature and for a sufficient length of time so as tosoften the thermoplastic film and the ethylene vinyl acetate such thatthe laminating pressure bonds said thermoplastic film to said ethylenevinyl acetate.
 7. The method of claim 6 comprising tacking the first andsecond thermoplastic films and fabric together so as to be lightlyadhered prior to the step of forming a wound bundle.
 8. The method ofclaim 6 further comprising providing a release paper in said woundbundle so as to provide separation between laminate and film layers inthe bundle.
 9. The method of claim 6 wherein the heating of the woundbundle is conducted at a temperature between about 200° F. and 285° F.for between about 8 and about 18 hours.
 10. The method of claim 6wherein heating the wound bundle is conducted at a temperature of about265° F. for about 8 hours.
 11. The method of claim 6 wherein the step ofheating the wound bundle is conducted at a temperature of between about200° F. and 285° F. for about 18 hours.
 12. The method of claim 6wherein the fabric and thermoplastic films are wound around a core, thecore having a diameter between about 2 inches and 6 inches.